Even though closed formulations (e.g. must, shall, is, etc) may be used in the following disclosure, this is not to be interpreted as essential features or facts without alternatives. Contrarily, the disclosure is to be interpreted as a number of examples and embodiments provided for illustrative and non-limiting purposes.
In current 3GPP (Third Generation Partnership Project) discussions, there are two different RSRQ (Reference Signal Receiver Quality) measurement methods, which are expected to be specified in TS 36.214, Release 12 version 12.0.0 (compare with TS36.214, Release 11, sec. 5.1.3). The use of this is dependent on specific scenario. For the use of RSRQ in general the UE (User Equipment, a type of wireless communication device) is required to measure RSRQ only in specific symbols containing CRS (Cell-specific Reference Signal). This is very restricted for the UE and also for the network node.
Signal Quality Measurement
A signal quality measurement comprises of both signal strength and interference components. Typically it is the ratio of signal strength and interference in linear scale and difference between signal strength and interference in log scale.
In general the quality measurement (Qrx) can be expressed as follows:
                              Q          rx                =                              P            rx                                I            +                          N              o                                                          (        1        )            
Where, Prx is the received power of pilot or reference signal (i.e. signal strength part), No is the noise power, and I is the interference. Depending upon the type of quality measurement the component I can be interference on the pilot or the total interference on the entire carrier or simply inter-cell interference plus noise.
The signal strength is typically measured on any kind of reference signal or pilot signal. The interference may include interference from one or several sources such as reference signals, control channels, data channels, noise etc. Examples of reference signals or pilot signals are primary synchronization signal (PSS), secondary synchronization signal (SSS), cell specific reference signal (CRS), reference signal (RS), channel state information reference signal (CSI-RS), positioning reference signal (PRS), demodulation reference signal (DM-RS), multimedia broadcast multicast service reference signal (MBMS RS), etc. Examples of signal quality are signal-to-noise ratio (SNR), signal-to-interference-and-noise ratio (SINR), reference signal received quality (RSRQ), common pilot channel energy per chip to noise power spectral density (CPICH Ec/No), channel state information (CSI), channel quality indication (CQI), channel state information reference signal received quality (CSI-RSRQ), etc.
The signal quality measurements (depending e.g. upon the measurement) may be performed on serving cell (or multiple serving cells in multi-carrier and/or coordinated multipoint (CoMP)) and one or more neighboring cells. The neighbor cells may belong to serving carrier frequency or non-serving carrier frequency. The non-serving carrier frequency can be inter-frequency or inter-RAT (radio access technology) carrier.
Furthermore the quality measurements (depending upon the measurement) may be performed by the UE in high activity RRC (radio resource control) state (e.g. RRC connected state, CELL_DCH state etc) and/or in low activity RRC states (e.g. idle state, CELL_PCH state, URA_PCH state, CELL_FACH state etc).
The RSRQ is typically used primarily for mobility in low (e.g. idle state, idle mode, URA_PCH state, CELL_PCH state etc) and high activity RRC states (e.g. connected state, CELL_FACH state, CELL_DCH state etc) in E-UTRAN and also in other systems for mobility with E-UTRAN.
In high activity state UE is known on cell level by the serving cell and can be typically scheduled by the serving cell.
Examples of other systems are UTRA FDD/TDD, GERAN/GSM, CDMA2000, HRPD, WLAN etc.
In low activity state the mobility scenario may comprise cell selection and cell reselection including intra-frequency, inter-frequency and inter-RAT (e.g. between UTRA to LTE (Long Term Evolution) etc). In high activity state example scenarios are cell change, handover, RRC connection re-establishment, RRC connection release with direction to target cell, primary component carrier (PCC) change in CA (carrier aggregation) or PCell (primary cell) change in CA etc.
Quality measurements including RSRQ may typically also be used for various applications other than mobility. Other example use cases are: positioning in general, enhanced cell ID (identity) positioning, fingerprinting positioning, minimization of drive tests (MDT), network planning, configuration and tuning of radio network parameters, self-organizing network (SON), network monitoring, interference management, determination and management of load, inter-cell interference control (ICIC) etc.
In low activity RRC state the UE may typically use quality measurement for autonomous actions e.g. cell reselection, logging results etc. In high activity RRC state the UE may typically report the measurements (e.g. in a mobility management measurement report) including RSRQ to the network node e.g. eNodeB, RNC (radio network controller), positioning node etc. The UE may, for example, report the quality measurement periodically, in an event triggered manner or on event triggered periodic manner.
RSRQ
Reference Signal Received Quality (RSRQ) is typically defined as the ratio N×RSRP/(E-UTRA carrier RSSI), where N is the number of resource blocks (RBs) of the E-UTRA carrier RSSI measurement bandwidth. The measurements in the numerator and denominator are preferably made over the same set of resource blocks.
Reference signal received power (RSRP) part of RSRQ is typically defined as the linear average over the power contributions (in [W]) of the resource elements that carry cell-specific reference signals within the considered measurement frequency bandwidth.
According to a typical application currently defined, RSSI measurements may be performed in two different variants.
According to the first variant (method), E-UTRA (LTE) Carrier Received Signal Strength Indicator (RSSI) in RSRQ comprises the linear average of the total received power (in [W]) observed only in OFDM (orthogonal frequency division multiplex) symbols containing reference symbols for antenna port 0, in the measurement bandwidth, over N number of resource blocks by the UE from all sources, including co-channel serving and non-serving cells, adjacent channel interference, thermal noise etc.
According to the second variant (method), if higher-layer signaling indicates certain subframes for performing RSRQ measurements, then RSSI is measured over all OFDM symbols in the indicated subframes. The higher layer signaling referred to herein may refer to the signaling of one or more measurement pattern to the UE for RSRQ measurements in heterogeneous network. The heterogeneous network typically comprises low and high power nodes. According to one example, the serving cell signals one or more measurement patterns (aka measurement resource restriction pattern) to inform the UE about the resources or subframes which the UE should use for performing measurements on a target victim cell (e.g. serving pico cell and/or neighboring pico cells). These resources or subframes within a measurement pattern where UE should measure RSRQ are protected from aggressor cell interference. These resources or subframes are also called restricted subframes or protected subframes.
These first and second variants (methods) will also be referred to below as respectively “old” and “new” mobility management measurement methods/RSRQ:s/methods/measurements/etc.
In various scenarios, mobility management measurements performed according to this approach may not be sufficiently accurate. Particularly, mobility management measurements performed according one or the other of the first and second methods may not be sufficiently accurate.
Therefore, there is a need for alternative approaches to mobility management measurements. Particularly, there is a need for approaches to selection between the first method and the second method in relation to various conditions.